Merge pull request #132 from bvssvni/master

Upgrade to latest Rust
Merge pull request #134 from bvssvni/master

Switched to GenericEvent
Cleaned up all_widgets examples, closes #131
Merge pull request #135 from mitchmindtree/master

Cleaned up all_widgets examples, closes #131
Updated to latest freetype-rs changes
Merge pull request #137 from mitchmindtree/master

Updated to latest freetype-rs changes
Added very basic support themes
Removed unnecessary printlns
Merge pull request #139 from mitchmindtree/master

Added early support for `Theme`s.
Changed positioning and dimensions over to [f64, ..2]
Merge pull request #146 from mitchmindtree/master

Changed positioning and dimensions over to [f64, ..2]
Added background drawing method to UiContext and updated example
Merge pull request #148 from mitchmindtree/master

Added background drawing method to UiContext and updated example.
Add Show trait as requirement for Drawable impl

I am unsure why this appears to be required, since the function val_to_string
only expects ToString, which implies Show. However, this seems to fix it at
least.
Merge pull request #149 from aepsil0n/fix/drawable_envelope_editor_context_show

Add Show trait as requirement for Drawable impl
Removed piston dependency

Closes https://github.com/PistonDevelopers/conrod/issues/152